1. Field of the Invention
The present invention relates to a color photographic photosensitive material for heat development.
2. Description of the Related Art
The technology for forming images by heat development of a silver halide photographic photosensitive material is well known. This technique is described, for example, in "Fundamentals of Photographic Engineering--Non-silver Salt Photography Section", pp.242-255, Corona Co., Ltd., 1982, U.S. Pat. No. 4,500,626, and others.
Because of its superior photographic properties such as its sensitivity and gradation in comparison with electrophotography and diazophotography, photography which uses heat developed photosensitive materials using silver halide is conventionally widely known. A variety of methods have been proposed for obtaining color images by heat development of a silver halide photosensitive material. One of these methods is a color development process in which color images are formed by the coupling reaction between the oxidized form of a developing agent and a coupler. As to the developing agents and the couplers usable in this color development system, there have been made various proposals. For example, U.S. Pat. No. 3,531,256 proposes a combination of a reducing agent based on a p-phenylenediamine and a phenol or an active methylene coupler; U.S. Pat. No. 3,761,270 proposes a reducing agent based on a p-aminophenol; and U.S. Pat. No. 4,021,240 proposes a combination of a reducing agent based on a sulfonamide and a 4-equivalent coupler.
However, in the conventional color development systems described above, since silver halides remain in undeveloped regions even after processing, color is sometimes formed in the undeveloped regions during printout or storage. In addition, since the reduced silver and the color images are present simultaneously in exposed regions, color muddiness is sometimes caused. Therefore, there is a need for improvement of these prior art color development systems.
In order to solve these problems, there has been proposed a dye transfer system in which diffusive dyes are formed by heat development and the dyes thus formed are then transferred to an image receiving layer. Among the modes of photosensitive materials for diffusion transfer heat development according to the above-described dye transfer system, there are a mode in which a photosensitive material has on the substrate thereof an image receiving layer capable of receiving dyes so that the photosensitive material has the ability to carry out the two functions (i.e., the dye-diffusing function and the dye-receiving function): and a mode in which a photosensitive material has no image receiving layer and is used in combination with an image receiving material having an image receiving layer provided on the substrate thereof.
When the dye transfer process is utilized in a color photographic photosensitive material intended for heat development, in order to obtain dye images having a high color purity, it is desirable to carry out the diffusion transfer of the dyes to the image receiving layer of the image receiving material simultaneously with the formation of the diffusive dyes or after the formation of the diffusive dyes in the color development of the photosensitive material.
On the other hand, there has been proposed a method in which diffusive dyes are released or formed image-wise in heat development so that the diffusive dyes are transferred to a fixing element. This method uses a dye-releasable (donative) compound which releases or forms a diffusive dye. According to this method, both a negative color image and a positive color image can be obtained by changing the type of dye-releasable compound or silver halide used. More details are described, for example, in U.S. Pat. Nos. 4,500,625, 4,483,914, 4,503,137, and 4,559,290, Japanese Patent Application Laid-Open (JP-A) Nos. 58-149,046, 60-133,449, 59-218,443, and 61-238,056, European Patent Application Laid-Open No. 220,746A2, Journal of Technical Disclosure No.87-6,199, and European Patent Application Laid-Open No. 210,660A2. The methods described in these publications, however, are associated with a problem that the sensitivity of the photosensitive material is reduced because a dye, which is colored in advance, is contained as a partial structure of the dye-releasable substance. In order to solve this problem, what is needed is the realization of a method in which a colorless coupler is present prior to development and the development causes a reaction between the colorless coupler and a developing agent to form a dye which is thereafter diffused.
Also proposed is a method in which diffusive dyes are produced by a coupling system so that an image is formed. For example, Japanese Patent Application Publication (JP-B) No. 63-36,487, and JP-A Nos. 5-224,381 and 6-83,005 disclose a photosensitive material for heat development which contains a precursor of a color developing agent capable of releasing p-phenylenediamine and a coupler; JP-A No. 59-111,148 discloses a combination of a ureidoaniline-based reducing agent and an active methylene-based coupler; JP-A No. 58-149,047 discloses a photosensitive material utilizing as a leaving group a coupler having a polymeric chain and releasing a diffusive dye in color development; and JP-A No. 9-152,705 discloses a technique in which a dye is formed/released by a combination of a carbamoylhydrazine-based developing agent and an active methylene-based coupler. However, the image forming methods utilizing a color developing agent or a precursor thereof and a dye-releasable substance described in these publications are associated with problems such as significant dependence on the processing time and therefore need improvements from the standpoint of speeding up the processing.
As a measure to solve these problems, for example, JP-A No. 1-138,556 discloses a method in which a hydrophilic reducing agent serving as an auxiliary developing agent is used together with a lipophilic reducing agent to allow electron transfer therebetween so that the development is speeded up. However, although this technique speeds up the development, it presents a serious problem that color muddiness is caused because, in some cases, the oxidized form of the auxiliary developing agent diffuses at the time of development into regions other than the color developing layer, which has been exposed, and thus develops color in these regions. To overcome this problem, as an ordinary measure, the reducing agent is immobilized between a color developing layer and another color developing layer. However, this measure, if utilized in the above-described processing methods, provides insufficient effects and, in addition, presents a problem that it seriously degrades the minimum density (D min) of the photosensitive material. From the foregoing, it will be appreciated that what is needed in the art is the advent of a technology which enables speedup in development while causing little or no color muddiness.